The applicant of the present application has disclosed a power supply device for a load on a timing device hand in Japanese Patent Application No. 63-233974. That device is constructed as follows. Two annular conductors are located below a hand and arranged in concentric relation therewith. A pair of conductors are attached to the lower surface of the hand and have contact segments slidable on the two annular conductors. The annular conductors are connected to an external circuit, and the conductors are connected to a load on the hand.
In this device, when electric power is supplied from the external circuit to the two annular conductors, the electric power is transferred to the pair of conductors by the contact segments slidable on the annular conductors, and further supplied to the load on the hand.
With such a brush conductor device, when the contact segments are slidably moved on the annular conductors, they cause frictional resistance to the rotation of the hand. An attempt can be made to adjust the pressure under which the contact segments are in contact with the annular conductors, to reduce such resistance. However, this may deteriorate the electrical connection therebetween.
Japanese Patent Application No. 63-331196 discloses a power supply device for the load of a hand that is intended to solve such problems of a brush conductor device. The power supply device uses a rotary transformer wherein a first coil is mounted to the lower surface of the hand, and a second coil is located downwardly and close to the first coil. Electric power is supplied from an external power source to the second coil to cause the first coil to produce an electromotive force. The power is then supplied from the first coil to the load on the hand.
The device is applied to a timepiece. Power is supplied from the external power source to an hour hand and a minute hand through a brush conductor device and to a second hand through the rotary transformer so as to cause electroluminescence elements on the hour, minute, and second hands to emit light.
It should be noted that the electroluminescence elements should be driven by a low-frequency signal to increase the life of the element, and that the rotary transformer should be driven by a high-frequency signal for improved efficiency of transfer of electric energy. If the high-frequency signal is fed to the electroluminescence element from an external power source, it shortens the life of the electroluminescence element. Also, if the low-frequency signal is fed to the rotary transformer, it deteriorates the efficiency of transfer of electric energy to the second hand.